<template>
  <div class="pagination">
    <!-- 上 -->
    <button :disabled="pageNo === 1" @click="$emit('getPageNo', pageNo - 1)">上一页</button>
    <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo', 1)" :class="{active: pageNo === 1}">1</button>
    <button v-if="startNumAndEndNum.start > 2">•••</button>
    <!-- 中间部分 -->
    <button v-for="(page, index) in startNumAndEndNum.end" :key="index" v-if="page>=startNumAndEndNum.start" @click="$emit('getPageNo', page)" :class="{active: pageNo === page}">{{page}}</button>
    <!-- 下 -->
    <button v-if="startNumAndEndNum.end < this.totalPage - 1">•••</button>
    <button v-if="startNumAndEndNum.end < this.totalPage" @click="$emit('getPageNo', totalPage)" :class="{active: pageNo === totalPage}">{{totalPage}}</button>
    <button :disabled="pageNo === totalPage" @click="$emit('getPageNo', pageNo + 1)">下一页</button>

    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
export default {
  name: 'Pagination',
  props: ['pageNo', 'pageSize', 'total', 'continues'],
  // 计算属性
  computed: {
    // 总共多少页
    totalPage() {
      return Math.ceil(this.total/this.pageSize)
    },
    // 计算出连续页码的起始数字和结束数字[连续的页码数：至少是5]
    startNumAndEndNum() {
      // 先定义两个变量存储起始数字和结束数字
      let start = 0
      let end = 0
      // 连续的页码数字是5【就是至少五页】，如果出现不正常的现象【不够五页】
      if(this.continues > this.totalPage){
        // 不正常现象
        start = 1
        end = this.totalPage
      } else {
        // 正常现象
        start = this.pageNo - parseInt(this.continues / 2)
        end = this.pageNo + parseInt(this.continues / 2)
        // 把出现不正常的现象【start数字出现0|负数】纠正
        if(start < 1) {
          start = 1
          end = this.continues
        }
        if(end > this.totalPage) {
          start = this.totalPage - this.continues + 1
          end = this.totalPage
        }
      }
      // 两个值，只能返回对象，key和value一致省略value
      return {start, end}
    }
  }
}
</script>

<style lang="less" scoped>
.pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
.active {
  background-color: skyblue;
}
</style>
